A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, School of Environment, Resources and Development

Thesis (M.Sc.) - Asian Institute of Technology, 1999

This study investigated treatment alternatives for COD wastewater from academic laboratories using a number of technologies including chemical reduction/precipitation, ion exchange and adsorption by chitosan. Results showed that high concentrations of 375 mg/l chromium, 1,740 mg/l mercury and 993 mg/l silver in COD wastewater can be reduced to 2.34 mg/l, 3.65 mg/l and 1.89 mg/l respectively, by the chemical reduction/precipitation process. Results from ion exchange at a flowrate of 20 ml/min showed that breakthrough effluent concentrations can be obtained at 0.59 mg/l chromium, 3.92 æ g/l mercury and 0.21 mg/l silver corresponding to 75.6 liters at 63 hours, 40.8 liters at 34 hours and 18 liters at 15 hours respectively. Kinetic and isotherm studies revealed that chitosan can adsorb Cr6 +, Hg2 + and Ag+ ions most effectively with a flowrate of 20 ml/min and the optimum pH for feed solution is 4. Chitosan column experiments indicated that average effluent concentrations at breakthrough point for chromium, mercury and silver are 1.76 mg/l, 89.42 æ g/l and 0.7 mg/l with tlu·oughput volumes and retention times of 120 liters at 100 hours, 180 liters at 150 hours and 48 liters at 40 hours. Results of solidification experiments based on compressive strength and metal leachability tests showed that the permissible and acceptable ranges of the solidification parameters were sludge/cement = 0.1 - 1.0 (weight/weight), water/cement = 0.5 - 0.6 (weight/weight) and sand/cement := 0.5 - 3.0 (weight/weight). Summary of the operating cost per liter of COD wastewater treated, based on the current prices in Thailand was found to be Baht 19 .95 for the chemical reduction/precipitation process, Baht 96.35 for ion exchange treatment and Baht 18.29 for chitosan adsorption.